Traditional servers today use a wide variety of storage technologies to store data, such as direct attached storage (DAS), network attach storage (NAS), and storage area network (SAN). Each storage technology may require a different type of data communication protocol to communicate data between the server and the selected type of storage technology. Legacy servers, cannot often communicate with each and every type of protocol and may be limited to DAS and NAS type storage.
Historically, servers were configured to boot their operating system from an internal storage device like a parallel small computer service interface (SCSI) hard disk or serial advanced technology adapter (SATA) hard disk, types of direct attached storage technology within a server or directly attached to it. A host bus adapter (HBA) with the appropriate communication protocol was often used to interface to the hard disks. An on-board or attached SCSI HBA or SATA HBA was used to access the hard disks of a server.
As data centers were introduced to support and share data by network storage devices, the local hard disks of a server were no longer used to store data. In many servers, the on-board or attached SCSI HBA or SATA HBA and hard disk was used as the boot device of the server, to start up the server with its operating system (OS) software.
The use of local storage only for operating system boot of a server became problematic, particularly as thousands of servers were introduced into data centers. The hard disk drive form factor also became an issue because the small form factor size of servers used in equipment racks. Disk-less servers became desirable.